Re: [PATCH 2/2] tpm: add backend for mssim

[Stefan Berger]

On 1/9/23 13:51, James Bottomley wrote:
> On Mon, 2023-01-09 at 13:34 -0500, Stefan Berger wrote:
> > On 1/9/23 12:55, James Bottomley wrote:
> > > On Mon, 2023-01-09 at 17:52 +0000, Dr. David Alan Gilbert wrote:
> > > > * James Bottomley (jejb@linux.ibm.com) wrote:
> > > [...]
> > > > > external MSSIM TPM emulator has to be kept running to preserve
> > > > > the state.  If you restart it, the migration will fail.
> > > >
> > > > Document that and we're getting there.
> > >
> > >
> > > The documentation in the current patch series says
> > >
> > > ----
> > > The mssim backend supports snapshotting and migration, but the
> > > state of the Microsoft Simulator server must be preserved (or the
> > > server kept running) outside of QEMU for restore to be successful.
> > > ----
> > >
> > > What, beyond this would you want to see?
> >
> > mssim today lacks the functionality of marshalling and unmarshalling
> > the permanent and volatile state of the TPM 2, which are both needed
> > for snapshot support. How does this work with mssim?
>
> You preserve the state by keeping the simulator running as the above
> says.  As long as you can preserve the state, there's no maximum time
> between snapshots.  There's no need of marshal/unmarshal if you do
> this

From https://lists.gnu.org/archive/html/qemu-devel/2022-12/msg03146.html

"VM snapshotting is basically VM suspend / resume on steroids requiring
permanent and volatile state to be saved and restoreable from possible very
different points in time with possibly different seeds, NVRAM locations etc.
How the mssim protocol does this is non-obvious to me and how one coordinates
the restoring and saving of the TPM's state without direct coordination by QEMU
is also non-obvious."


   Stefan
.
> James